Method for recovering carbon dioxide and recovery apparatus therefor

Abstract

To provide a method for recovering carbon dioxide and a recovery apparatus therefor that enable continuous recovery of the carbon dioxide, reduction of energy needed for the recovery, and compactness of the recovery apparatus.SOLUTION: A method for recovering carbon dioxide as a liquid from a gas containing the carbon dioxide comprises a pressurizing step of pressurizing the gas to 0.52 MPa or higher, a liquefying step of cooling the carbon dioxide in the pressurized gas to liquefy it, and an accumulating step of collecting and recovering the liquefied carbon dioxide. In the liquefying step, the carbon dioxide in the gas is brought into contact with a cooled porous structure to be liquefied. Also provided is a carbon dioxide recovery apparatus for use in the method for recovering the carbon dioxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for recovering carbon dioxide. [Background technology]

[0002] In recent years, in order to prevent global warming, it has become an increasingly urgent issue to curb emissions of greenhouse gases, including carbon dioxide. Greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and hydrofluorocarbons (HFCs). S ), perfluorocarbons (PFCs) S ), and sulfur hexafluoride (SF6). Considering the global warming potential and atmospheric concentration, carbon dioxide is the greenhouse gas that contributes most to global warming among these gases.

[0003] Other than automobile exhaust gases, major sources of carbon dioxide emissions include industrial exhaust gases emitted from heating furnaces, combustion furnaces, incinerators, boilers, etc. at thermal power plants, steel mills, chemical plants, etc. Therefore, various carbon dioxide capture technologies have been investigated to reduce the amount of carbon dioxide emitted from these industrial exhaust gases.

[0004] Known carbon dioxide separation and capture technologies include chemical absorption, physical absorption, membrane separation, physical adsorption, and cryogenic separation. Of these, chemical absorption has been the most widely researched and has been adopted by major domestic companies, with large commercial plants also in operation.

[0005] Here, we focused on carbon dioxide separation and capture technology using cryogenic separation, which has not received much attention until now. There is already a large amount of prior art for carbon dioxide separation and capture technology using cryogenic separation. For example, Patent Document 1 discloses a method and device for separating carbon dioxide and other substances from combustion gases emitted from pressurized combustion devices that pressurize and burn combustion systems such as boilers and furnaces, by cryogenic separation. Furthermore, Patent Document 2 discloses a carbon dioxide capture method and capture device that separates and concentrates carbon dioxide from gases containing carbon dioxide, such as combustion gases, by cryogenic separation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 4-334704 [Patent Document 2] Patent No. 6834515 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method of Patent Document 1 employs a method of expanding exhaust gas in a gas turbine as a cooling method. In this case, the gas turbine is a large device that rotates at high speed, and installation and management of the device require a great deal of cost and energy. In addition, the recovery device described in Patent Document 2 has a complex configuration, making it difficult to make it into a small device.

[0008] The present invention has been made in view of the above-described circumstances. That is, an object of the present invention is to provide a carbon dioxide capture method and capture device that can continuously capture carbon dioxide, reduce the energy required for capture, and make the capture device compact. [Means for solving the problem]

[0009] Considering the handling, storage, and transportation of carbon dioxide after capture, it is desirable to capture carbon dioxide as a liquid. According to the phase diagram of carbon dioxide, carbon dioxide can exist as a liquid at temperatures higher than its triple point (-56.6°C) and pressures higher than its triple point (0.518 MPa). Therefore, we investigated the configuration of a capture device that can achieve an environment where the temperature and pressure are higher than the triple point of carbon dioxide.

[0010] Conventionally, the Stirling cycle, the Gifford-McMahon cycle (GM cycle), and the pulse tube refrigeration cycle have been known as compact refrigerators. Of these, the Stirling cycle is, in principle, the most energy efficient. A cooling device using the Stirling cycle is called a Stirling cooler.

[0011] In order to continuously and efficiently cool a large amount of gas to a low temperature, how to reduce the energy required for cooling is an important practical point. As a result of extensive research, the inventors of the present invention have decided to use a Stirling cooler as the cooling means, which has superior energy efficiency compared to other cooling means.

[0012] The present invention has been achieved based on the above findings. That is, the present invention has the following configuration.

[0013] The carbon dioxide recovery method of the present invention is a carbon dioxide recovery method for recovering carbon dioxide as a liquid from a gas containing carbon dioxide, and includes a pressurizing step of pressurizing the gas to 0.52 MPa or more, a liquefaction step of cooling and liquefying the carbon dioxide in the pressurized gas, and a collection step of collecting and recovering the liquefied carbon dioxide. In the liquefaction step, the carbon dioxide in the gas is liquefied by contacting it with a cooled porous structure. In the liquefaction step, it is preferable to cool the porous structure to −10°C to −56°C using a Stirling cooler. The method may further include a moisture removal step of removing moisture from the gas before the pressurizing step. The method may further include a pre-cooling step of cooling the gas before the moisture removal step. The method may further include a pre-cooling step of pre-cooling the pressurized gas between the pressurizing step and the liquefaction step.

[0014] The carbon dioxide recovery apparatus of the present invention is a carbon dioxide recovery apparatus that recovers carbon dioxide as a liquid from a gas containing carbon dioxide, and includes a pressurizing device that pressurizes the gas to 0.52 MPa or more, a liquefaction device that liquefies the carbon dioxide in the pressurized gas by bringing it into contact with a cooled porous structure, and an accumulation device that collects and recovers the liquefied carbon dioxide. Here, it is preferable that the porous structure is cooled to -10°C to -56°C using a Stirling cooler. Furthermore, a moisture removal device that removes moisture from the gas may be provided before the pressurizing device. Furthermore, a pre-cooling device that cools the gas may be provided before the moisture removal device. Furthermore, a pre-cooling device that pre-cools the pressurized gas may be provided between the pressurizing device and the liquefaction device. [Effects of the Invention]

[0015] The carbon dioxide recovery method and recovery device of the present invention are capable of recovering carbon dioxide continuously, reducing the energy required for recovery, and making the recovery device compact. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram of a carbon dioxide recovery device according to an embodiment of the present invention. [Figure 2] 2A and 2B are schematic diagrams of a liquefaction device and an accumulation device of a modified example of a carbon dioxide capture device according to an embodiment of the present invention. In Fig. 2A, the three-dimensional shape of the porous structure is cylindrical. In Fig. 2B, the three-dimensional shape of the porous structure is rectangular. In Fig. 2C, the three-dimensional shape of the porous structure is cubic. In Fig. 2D, the three-dimensional shape of the porous structure is spherical. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail, but the embodiments of the present invention are not limited to the specific embodiments described below.

[0018] In this embodiment, the gases containing carbon dioxide that are the target of the method and apparatus for recovering carbon dioxide are not only automobile exhaust gases and exhaust gases emitted from various industrial facilities, but also, if possible, the air with a low concentration of carbon dioxide.

[0019] (Stirling cooler) The present inventors employ a Stirling cooler (Stirling refrigerator) as a cooling means for cooling carbon dioxide in a gas containing carbon dioxide (hereinafter sometimes simply referred to as "gas"). A Stirling engine is a type of heat engine, and is a closed external combustion engine that converts thermal energy into mechanical energy. By reversing the cycle of this Stirling engine, it functions as a refrigerator (Stirling cooler).

[0020] Among the Stirling coolers, the β-type Stirling cooler, in which the displacer and power piston are arranged in the same cylinder, is preferable because it can be made smaller. In the β-type Stirling cooler, a linear motor is driven by external power to drive the piston and displacer in coordination, expanding and compressing gas such as helium inside the engine, and cooling the cooling head part by the thermosiphon principle. Furthermore, free-piston Stirling coolers, which use gas bearings and operate without physical contact (friction) and without wear on moving parts, are more preferable because they have a longer life and are more energy efficient.

[0021] The free-piston Stirling cooler is a sealed system that can rapidly cool the cooling head down to -100°C or below in a short time by simply supplying external power. It can also be made into a lightweight and compact device. For these reasons, it is preferable to use a free-piston β-type Stirling cooler in this embodiment. The thermal energy absorbed by the cooling head is discharged to the outside from the rear of the device.

[0022] (Method of capturing carbon dioxide) The carbon dioxide recovery method of this embodiment includes a pressurizing step of pressurizing a gas containing carbon dioxide to 0.52 MPa or more, a liquefaction step of liquefying the carbon dioxide in the pressurized gas by contacting it with a cooled porous structure, and a collection step of collecting and recovering the liquefied carbon dioxide. Here, in the liquefaction step, it is preferable that the porous structure is cooled to -10°C to -56°C using a Stirling cooler. It is also preferable that a moisture removal step of removing moisture from the gas is included before the pressurizing step. It is also preferable that a pre-cooling step of cooling the gas is included before the moisture removal step. It is also preferable that a pre-cooling step of pre-cooling the pressurized gas is included between the pressurizing step and the liquefaction step.

[0023] Each step of the carbon dioxide recovery method of this embodiment, i.e., the pre-cooling step, moisture removal step, pressurizing step, pre-cooling step, liquefaction step and accumulation step, can be carried out by each of the devices of the carbon dioxide recovery apparatus, namely, the pre-cooling device, moisture removal device, pressurizing device, pre-cooling device, liquefaction device and accumulation device, as described below.

[0024] (Carbon dioxide capture device) FIG. 1 shows a schematic configuration diagram of a carbon dioxide recovery device according to an embodiment of the present invention. The carbon dioxide capture system of this embodiment mainly comprises a pre-cooling device 1 that cools a gas containing carbon dioxide, a moisture removal device 2 that removes moisture from the pre-cooled gas, a pressurizing device 3 that pressurizes the dehydrated gas to 0.52 MPa or higher, a pre-cooling device 4 that pre-cools the pressurized gas, a liquefaction device that liquefies the carbon dioxide in the pre-cooled gas by contacting it with a cooled porous structure, and an accumulation device that collects and recovers the liquefied carbon dioxide. The liquefaction device and accumulation device are housed in a pressure vessel 5. Here, the porous structure is cooled to -10°C to -56°C using a Stirling cooler. The storage device for storing the recovered carbon dioxide comprises a liquefied carbon dioxide tank 24 and a carbon dioxide gas cylinder 28.

[0025] When the temperature of the gas containing carbon dioxide is room temperature or below 30° C., the pre-cooling device 1 is not particularly necessary, and the gas is first introduced into the moisture removing device 2. However, when the gas temperature exceeds 30°C, if the gas is introduced directly into the moisture removal device 2, the gas temperature cannot be sufficiently lowered, and there is a risk that the moisture in the gas will not be sufficiently removed. Therefore, when the gas temperature exceeds 30°C, a pre-cooling device 1 is installed to lower the gas temperature to 30°C or below.

[0026] The method for cooling the gas in the pre-cooling device 1 is not particularly limited. Various existing methods, such as air-cooling and water-cooling, can be appropriately selected and used. FIG. 1 shows a schematic diagram of a pre-cooling device 1 using an air-cooling method. A metal gas pipe 10 is installed inside the pre-cooling device 1, and multiple metal fins 11 are attached to the pipe. Air is taken in through an inlet 12 by a fan 13 and discharged through an outlet 14. By circulating air around the outside of the gas pipe 10 inside the pre-cooling device 1, the gas pipe 10 and the gas inside the pipe can be cooled. The multiple metal fins 11 attached to the pipe allow for efficient heat exchange and cooling of the gas.

[0027] As a cooling method for the pre-cooling device 1, after liquefying carbon dioxide in the liquefaction step, a portion of the exhaust gas discharged from the liquefaction step can be used as a cooling source for the pre-cooling step (not shown), as will be described later. Furthermore, a portion of the exhaust gas used as a cooling source for the pre-cooling step or a portion of the exhaust gas used as a cooling source for the moisture removal step can be used as a cooling source for the pre-cooling step (not shown). In these cases, a portion of the exhaust gas is used in place of air in the above-mentioned air-cooling method.

[0028] In this way, by recycling the exhaust gas discharged in the subsequent liquefaction process and using it in a cascade manner as a cooling source in multiple processes before the liquefaction process, it is possible to reduce the energy required for cooling. However, since the exhaust gas discharged in the liquefaction process is in a high-pressure state, it is necessary to take measures to appropriately reduce the pressure using a known method, as necessary. Also, although it is stated that "a part of the exhaust gas" is used, some or all of the exhaust gas can be used as necessary (the same applies to other descriptions).

[0029] The gas cooled in the pre-cooling device 1 is then introduced into the moisture removal device 2. If the gas contains moisture, this is undesirable because it will reduce the thermal conductivity of the liquefaction device when the gas is further cooled to a low temperature to recover carbon dioxide, thereby reducing the cooling efficiency and the purity of the liquefied carbon dioxide.

[0030] In the moisture removal device 2, the method for removing moisture from gas is not particularly limited as long as it does not involve heating the gas. Various existing methods, such as the use of a moisture absorbent, an adsorption method, or a cooling method, can be appropriately selected and used. Known moisture absorbents include silica gel, alumina, molecular sieves, zeolite, and activated carbon. Figure 1 shows a schematic diagram of the structure of a moisture removal device 2 using a cooling method. Specifically, a cooling base 17 is installed at the top inside the housing 15 of the moisture removal device 2, and multiple metal perforated plates 16 are attached to the bottom of the cooling base 17, so that the removed moisture drips from the metal perforated plates 16 and accumulates at the bottom.

[0031] The metal perforated plate 16 is made of a metal with good thermal conductivity, such as iron, stainless steel, copper, or aluminum. The metal perforated plate 16 is designed to have as large a surface area as possible so that, when gas passes through, water vapor in the gas comes into contact with the metal perforated plate 16, and the water vapor becomes liquid or solid and adheres to the surface of the metal perforated plate 16. For example, the metal perforated plate 16 may be made of a thin metal plate having a large number of fine holes formed on the entire surface thereof, and multiple metal plates with holes at different positions stacked at predetermined intervals, or multiple mesh-like woven fabrics formed from thin metal monofilaments stacked at predetermined intervals. The shape of the metal perforated plate 16 may be a flat plate, a bent plate, a three-dimensional porous solid, or a combination thereof, and is not particularly limited. A plurality of metal perforated plates 16 are stacked in parallel at a predetermined interval below the cooling base 17, and the internal structure and gas flow of the housing 15 of the moisture removal device 2 are controlled so that gas can pass through the thickness direction of the plurality of metal perforated plates 16.

[0032] The plurality of metal perforated plates 16 are cooled to a range of approximately 0 to -20°C by the cooling base 17. When the gas introduced into the moisture removal device 2 comes into contact with the plurality of metal perforated plates 16, the contained water vapor becomes liquid or solid and adheres to the surfaces of the metal perforated plates 16. The moisture that adheres to the surfaces of the metal perforated plates 16 then turns into droplets, flows down the surfaces of the metal perforated plates 16, and accumulates at the bottom of the housing 15. When the water that has accumulated at the bottom reaches a predetermined amount, it is stored in the water tank 18. The temperature of the metal perforated plates 16, the flow rate of the gas, the shape of the metal perforated plates 16, and the like are appropriately controlled so that the moisture that has adhered to the surfaces of the metal perforated plates 16 turns into droplets and flows down the surfaces of the metal perforated plates 16.

[0033] There are no particular limitations on the method for cooling the moisture removal device 2. However, as will be described later, after liquefying carbon dioxide in the liquefaction step, it is possible to use, as a cooling source for the moisture removal step, a portion of the exhaust gas discharged from the liquefaction step or a portion of the exhaust gas used as a cooling source in the pre-cooling step. 1, the cooling base 17 of the moisture removal device 2 is cooled by a portion of the exhaust gas used as a cooling source in the pre-cooling step, which is supplied through the pipe 33. As a result, the energy required to cool the moisture removal device 2 can be reduced. In FIG. 1, the exhaust gas used as a cooling source for the cooling base 17 of the moisture removal device 2 is then discharged as exhaust gas.

[0034] The gas from which moisture has been removed by the moisture remover 2 is then pressurized to 0.52 MPa or higher by the pressurizing device 3. In other words, the gas pressure is set to a pressure higher than the triple point of carbon dioxide (0.518 MPa). The pressurizing device 3 is a device that can continuously pressurize the gas, and is a so-called compressor. There are no particular limitations on the type of compressor. Any of the various existing compressors, such as reciprocating, rotary, centrifugal, and axial flow types, can be appropriately selected and used.

[0035] The temperature of the gas increases when the gas is pressurized by the pressurizing device 3. Therefore, it is preferable to pre-cool the gas whose temperature has increased before introducing the gas into the liquefaction device. Therefore, the pressurized gas is pre-cooled by the pre-cooling device 4.

[0036] The method for pre-cooling the gas in the pre-cooling device 4 is not particularly limited. Various methods, such as a cold air method or a refrigerant method, can be appropriately selected and used. FIG. 1 shows a schematic diagram of a pre-cooling device 4 using the cold air method. Specifically, a metal gas pipe 19 is installed inside the pre-cooling device 4, and a number of metal fins 20 are attached to the pipe. Attaching a number of metal fins 20 to the pipe enables efficient heat exchange and cooling of the gas.

[0037] In the pre-cooling device 4, it is preferable to use a portion of the exhaust gas discharged from the liquefaction step after recovering carbon dioxide in the accumulation step described below as a cooling source for cooling the interior of the pre-cooling device 4. A portion of the exhaust gas discharged from the liquefaction step is supplied to the pre-cooling device 4 through piping 32. As a result, it is possible to reduce the energy required for cooling the pre-cooling device 4. From the viewpoint of cooling efficiency, it is preferable that the portion of the exhaust gas discharged from the liquefaction step is introduced into the pre-cooling device 4 from a direction intersecting the direction in which the gas advances within the pre-cooling device 4. In the pre-cooling device 4, the gas is preferably cooled to 0 to -30°C.

[0038] FIG. 1 shows a schematic diagram of the structure of a pressure vessel 5. In this embodiment, the interior of the housing 21 of the pressure vessel 5 is divided into three regions having similar structures. The number of regions inside the housing 21 of the pressure vessel 5 is not particularly limited. The number of regions may be one or two or more, as necessary. A Stirling cooler cooling head 23 is installed above each region, and a plurality of porous structures 22 are attached to the bottom of the Stirling cooler cooling head 23. Liquefied carbon dioxide drips from the porous structures 22 at the bottom of each region and collects and accumulates as liquefied carbon dioxide.

[0039] The gas introduced into the pressure vessel 5 passes through the inside of the housing 21 to which a plurality of porous structures 22 are attached. The pressure inside the liquefaction device in the pressure vessel 5 is higher than the triple point of carbon dioxide (0.518 MPa). The pressure inside the liquefaction device is preferably 0.52 to 3.0 MPa, more preferably 1.0 to 2.0 MPa. The porous structure 22 is connected to the cooling head 23 of a Stirling cooler via a metal member with good thermal conductivity, and is cooled by the Stirling cooler. The cooling temperature is in a range higher than the triple point of carbon dioxide (-56.6°C), preferably -10°C to -56°C, more preferably -20°C to -50°C. Therefore, the carbon dioxide in the gas is liquefied by coming into contact with the porous structure 22 and adheres to the surface of the porous structure 22. The liquefied carbon dioxide that has adhered to the surface of the porous structure 22 flows downward along the surface of the porous structure 22 and falls downward as droplets from the bottom end of the porous structure 22. As a result, the carbon dioxide in the gas is recovered as liquefied carbon dioxide and accumulates at the bottom of the casing 21. In this way, the process of liquefying and accumulating the carbon dioxide in the gas is carried out within the casing 21 of the pressure vessel 5. The devices corresponding to each process are the liquefaction device and the accumulation device.

[0040] The porous structure 22 is made of a metal with good thermal conductivity, such as iron, stainless steel, copper, or aluminum. The porous structure 22 is configured to have as large a surface area as possible so that when the gas passes through, the gas comes into contact with the porous structure 22, and carbon dioxide in the gas liquefies and adheres to the surface of the porous structure 22. For example, a thin metal plate having many fine holes formed on the entire surface, and multiple metal plates with holes at different positions stacked at predetermined intervals, or a mesh-like woven fabric formed from thin metal monofilaments stacked at predetermined intervals, may be used. The shape of the porous structure 22 may be a flat plate, a bent plate, a three-dimensional porous solid, or a combination thereof, and is not particularly limited. A plurality of flat porous structures 22 are stacked in parallel at a predetermined interval below the cooling head portion 23 of the Stirling cooler in each region, and the structure and gas flow inside the housing 21 of the pressure vessel 5 are controlled so that the gas permeates in the thickness direction of the plurality of porous structures 22 and also permeates through the three regions sequentially.

[0041] The liquefied carbon dioxide that has accumulated at the bottom inside the casing 21 of the pressure vessel 5 is then stored in a liquefied carbon dioxide tank 24 when it reaches a predetermined amount. The temperature of the porous structure 22, the flow rate of the gas, the shape of the porous structure 22, etc. are appropriately controlled so that the liquefied carbon dioxide that has adhered to the surface of the porous structure 22 turns into drops and flows down the surface of the porous structure 22.

[0042] The liquefied carbon dioxide stored in the liquefied carbon dioxide tank 24 can be transferred in liquid form from the liquefied carbon dioxide tank 24 to a low-temperature pressure vessel and transported to the outside. The liquefied carbon dioxide stored in the liquefied carbon dioxide tank 24 can also be transferred to a liquefied carbon dioxide evaporator 26 through an on-off valve 25, where it is changed from a liquid to a gas, and then passed through an on-off valve 27 and stored in a carbon dioxide gas cylinder 28. The stored carbon dioxide can be transported to the outside as the carbon dioxide gas cylinder 28. As the liquefied carbon dioxide evaporator 26, any known device can be appropriately selected and used.

[0043] The gas remaining after carbon dioxide has been recovered from the gas in the accumulation device is discharged from the pressure vessel 5 as exhaust gas discharged from the liquefaction process through piping 29. The exhaust gas may be discharged as exhaust gas from piping 31 via a three-way valve 30, or may be supplied to a pre-cooling device 4 or the like as a cooling source through piping 32. In this way, the exhaust gas discharged from the pressure vessel 5 is circulated and used in a cascade manner as a cooling source for the pre-cooling step, moisture removal step and pre-cooling step prior to the liquefaction step, thereby reducing the energy required for cooling in the carbon dioxide recovery system.

[0044] A control device (not shown) is installed to control the overall functions of each device that makes up the carbon dioxide capture system of this embodiment, namely the pre-cooling device 1, moisture removal device 2, pressurizing device 3, pre-cooling device 4, liquefaction device, accumulation device, and storage device. To control the functions of each device, a thermometer, pressure gauge, hygrometer, flow meter, carbon dioxide concentration meter, level gauge, etc. are installed at appropriate points in the system and controlled by the control device.

[0045] (Modification 1 of this embodiment) Fig. 2 shows a schematic configuration diagram of a liquefaction device and an accumulation device of a modified example of the carbon dioxide capture device of this embodiment. Fig. 2 shows modified examples (a) to (d) of the three-dimensional shape of the porous structure 22 inside the casing 21 of the pressure vessel 5 in the carbon dioxide capture device shown in Fig. 1. The number of internal regions of the casing 21 of the pressure vessel 5 is one. In FIG. 2(a), the porous structure 41 has a cylindrical (or columnar) three-dimensional shape. It is a three-dimensional porous structure constructed using thin metal filaments, a thin metal plate with numerous fine holes, or the like. The porous structure 41 is cooled by a Stirling cooler (not shown). One of the left faces of the cylindrical porous structure 41 is covered with a metal flat plate 42. A pipe 43 is installed in the center of the plate, and exhaust gas is introduced into the porous structure 41 through the pipe 43. As the exhaust gas passes through the porous structure 41, carbon dioxide in the exhaust gas comes into contact with the porous structure 41, is cooled, and is liquefied, and adheres to the surface of the porous structure 41. The liquefied carbon dioxide then flows downward along the surface of the porous structure 41 and falls downward as droplets from the bottom end of the porous structure 41. The liquefied carbon dioxide accumulates and accumulates at the bottom 47 of the housing 40. The accumulated liquefied carbon dioxide is discharged to the outside of the housing 40 via piping 46. On the other hand, the exhaust gas passes through the porous structure 41, is accumulated on the accumulation plate 45, and is discharged to the outside of the housing 40 via piping 44.

[0046] In Fig. 2(b), the three-dimensional shape of the porous structure 41 is a rectangular parallelepiped. The detailed description is the same as that of Fig. 2(a). In Figure 2(c), the three-dimensional shape of the porous structure 41 is a cube. Exhaust gas is introduced into the porous structure 41 through a pipe 43. The pipe 43 has an outlet in a spherical space 48 near the center of the cubic porous structure 41. Therefore, the exhaust gas discharged from the pipe 43 passes through the porous structure 41 from the spherical space 48 toward the periphery. The exhaust gas that has passed through the porous structure 41 is collected on the collection plate 45 and is discharged to the outside of the housing 40 via a pipe 44. Other explanations are omitted as they are the same as those in Figure 2(a). In Fig. 2(d), the three-dimensional shape of the porous structure 41 is a sphere. The detailed description is the same as that of Fig. 2(c).

[0047] (Modification 2 of this embodiment) In the above embodiment, in order to reduce the energy required for cooling in the carbon dioxide capture device, a method was shown in which a portion of the exhaust gas discharged in the liquefaction process was recycled and used as a cooling source for the pre-cooling process, the moisture removal process, and the pre-cooling process. In this case, in the pre-cooling step and the pre-cooling step, the gas is cooled by heat exchange between the gas and the exhaust gas via a heat exchanger. In contrast to this, the modified example of this embodiment is the following method. In the pre-cooling step, the moisture removal step and the pre-cooling step, a method can be carried out in which part or all of the exhaust gas discharged in the liquefaction step is directly mixed with the gas in the pipe (not shown). In this case, since the exhaust gas discharged from the liquefaction process is in a high pressure state, it is necessary to take measures to reduce the pressure appropriately by a known method, if necessary. The method for mixing the gas and part or all of the exhaust gas is not particularly limited, and can be appropriately selected from known methods, such as a method of injecting part or all of the exhaust gas into the gas in the housing, or a method of mixing and then stirring, so that the two types of gas are mixed uniformly. The mixing ratio of the gas and a part or all of the exhaust gas can be appropriately set depending on the temperatures of both and the purpose of each step.

[0048] In this embodiment, carbon dioxide has been mainly described as the target substance to be recovered from gas. However, nitrous oxide is another greenhouse gas with similar properties to carbon dioxide. Nitrous oxide has a global warming potential approximately 300 times that of carbon dioxide, making its recovery highly significant. At atmospheric pressure, the melting point of nitrous oxide is -90.9°C, and the boiling point is -88.5°C, both of which are close to the sublimation temperature of carbon dioxide, which is -78.5°C. Therefore, by using the method and apparatus of this embodiment, it is possible to recover nitrous oxide along with carbon dioxide. Furthermore, because the melting or boiling points of nitrogen dioxide, sulfur dioxide, and sulfur trioxide are higher than that of nitrous oxide, they can be recovered simultaneously with nitrous oxide. Therefore, the method and apparatus of this embodiment have the advantage of being able to simultaneously recover and remove not only carbon dioxide but also nitrogen oxides and sulfur oxides from exhaust gases emitted from plants, etc.

[0049] As can be seen from the above description, the carbon dioxide recovery method and recovery device of this embodiment have the following features. (1) The present recovery method and recovery device can continuously recover carbon dioxide from a gas containing carbon dioxide. (2) This recovery method and recovery device require less energy to operate, are easier to maintain, and produce less noise and vibration because they have fewer moving parts. (3) This recovery method and recovery device cool only the gas that comes into contact with the porous structure cooled to a low temperature, and liquefy only the carbon dioxide contained therein. Since the entire gas containing carbon dioxide is not cooled to a low temperature, the energy required for cooling can be reduced. (4) The present recovery method and recovery device can reduce the energy required for cooling by using a Stirling cooler. (5) This recovery method and recovery device can recover not only carbon dioxide but also nitrous oxide, nitrogen dioxide, sulfur dioxide, and sulfur trioxide. (6) The present recovery method and recovery device can be made compact, allowing for a high degree of freedom in the location of installation. Therefore, they can be installed in a variety of exhaust gas emission facilities, regardless of their size. [Explanation of symbols]

[0050] 1 Precooler 2 Moisture removal device 3. Pressure device 4. Backup cooling device 5. Pressure vessels 10 Piping 11 Finn 12 Intake port 13 Fan 14 Outlet 15 Case 16 Metal perforated plate 17 Cooling base 18 Water Tank 19 Piping 20 Finn 21. Cabinet 22 Porous structure 23 Cooling head 24 Liquefied carbon dioxide tank 25 Opening and closing valve 26 Liquefied carbon dioxide evaporator 27 Opening and closing valve 28 Carbon dioxide gas cylinder 29 Piping 30 Three-way valve 31 Piping 32 Piping 33 Piping

Claims

1. A method for recovering carbon dioxide in the form of a liquid from a gas containing carbon dioxide, comprising: a pressurizing step of pressurizing the gas to 0.52 MPa or more; a liquefaction step of cooling and liquefying the carbon dioxide in the pressurized gas; and an accumulation step of collecting and recovering the liquefied carbon dioxide, A method for recovering carbon dioxide, wherein in the liquefaction step, the carbon dioxide in the gas is brought into contact with a cooled porous structure to be liquefied.

2. 2. The method for recovering carbon dioxide according to claim 1, wherein in the liquefaction step, the porous structure is cooled to −10° C. to −56° C. using a Stirling cooler.

3. 3. The method for recovering carbon dioxide according to claim 1, wherein the porous structure is made of a metal.

4. 3. The method for recovering carbon dioxide according to claim 1, further comprising a moisture removal step of removing moisture from the gas before the pressurizing step.

5. 5. The method for recovering carbon dioxide according to claim 4, further comprising a pre-cooling step of cooling the gas before the moisture removal step.

6. 3. The method for recovering carbon dioxide according to claim 1, further comprising a pre-cooling step of pre-cooling the pressurized gas between the pressurizing step and the liquefaction step.

7. A carbon dioxide recovery device that recovers carbon dioxide as a liquid from a gas containing carbon dioxide, a pressurizing device that pressurizes the gas to 0.52 MPa or more; a liquefaction device that liquefies the carbon dioxide in the pressurized gas by contacting it with a cooled porous structure; and a collection device for collecting and recovering the liquefied carbon dioxide.

8. 8. The carbon dioxide recovery device according to claim 7, wherein the porous structure is cooled to −10° C. to −56° C. using a Stirling cooler.

9. 9. The carbon dioxide recovery system according to claim 7, further comprising a moisture removal device for removing moisture from the gas, the moisture removal device being provided before the pressurization device.

10. 10. The carbon dioxide recovery system according to claim 9, further comprising a pre-cooling device for cooling the gas, the pre-cooling device being provided before the moisture removal device.

11. 9. The carbon dioxide recovery system according to claim 7, further comprising a pre-cooling device between the pressurizing device and the liquefaction device, the pre-cooling device pre-cooling the pressurized gas.

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